1. Field of the Invention
The present invention relates to a cover structure for the power transmission device of a motorcycle or the like.
2. Discussion of the Relevant Art
Many motorcycles employ a belt-and-pulley power transmission device since the engine output power and the torque transmitted to the drive wheel are relatively small. The belt-and-pulley power transmission device generally comprises a driver pulley mounted on the output shaft of the engine, a driven pulley drivable by the driver pulley, and a belt for transmitting the rotative power from the driver pulley to the driven pulley. The belt-and-pulley power transmission device is housed in a casing installed on the rear portion of a motorcycle frame. The casing, which doubles as part of a crankcase, also accommodates a kick starter for the engine. The casing is of a fully closed construction with its opening covered by a case cover fastened by bolts to the casing. The casing is however disadvantageous in that it vibrates when the engine vibrates, and such vibration is transmitted to the case cover, generating undesired noise.
Various attempts have heretofore been made to prevent such vibration-induced noise. For example, Japanese Laid-Open Utility Model Publication No. 59/127956 discloses a casing with a case cover fixed thereto by bolts through a packing, the bolts being associated with vibro-isolating members of a resilient material. Each of the bolts has a flange to limit the inserted position of the bolt in the casing for thereby preventing the vibro-isolating member from being deformed under pressure.
The above arrangement is effective in reducing, to some extent, the noise arising from vibration of the case cover. However, the noise reduction capability of the conventional cover structure according to the above arrangement is insufficient since only the resilient vibro-isolating members are interposed between the case cover and the bolts. Additionally, the cover structure according to the above arrangement has another drawback in that its overall rigidity is greatly reduced because of the resilient vibro-isolating members, and hence an engine starter cannot be attached directly to the case cover.